ESSAYS ON BACTERIOLOGY. 141 



20 to 30 per cent, solutions of nitric acid. As con- 

 trast color, methyl blue is used in watery solution. 

 To hasten the process in everyday work the carbol- 

 fuchsin solution is applied hot, and to further save 

 time the decolorizing and counter-staining are accom- 

 plished in one operation by combining the methyl 

 blue and 25 per cent, sulphuric acid. In detail the 

 process is as follows: Having spread the suspicious 

 material upon cover glasses, dried and heated them, 

 by the method already described, the dye is dropped 

 upon the glass and the latter held by forceps over a 

 clean flame until steam rises. If evaporation occur 

 to dryness, more of the dye is added. A better 

 method, though more wasteful of staining solution, is 

 to heat the dye in a dish, floating the cover glasses 

 upon the liqitid. After two or three minutes' ex- 

 posure to the dye, the glasses are rinsed in water, 

 washed in the acid solution till the color fades out, 

 then in alcohol for a few 'seconds to wash out the al- 

 tered dye, and then thoroughly rinsed in water to re- 

 move the acid and alcohol. If examined at this stage 

 the tubercle bacilli will be seen stained red, other bac- 

 teria being colorless. To counter-stain the specimen 

 it is subjected for flfteen to thirty seconds to a watery 

 solution of methyl blue, after which it is again rinsed 

 in water. Inverted over a drop of distilled water and 

 examined, the tubercle bacilli will be found still red, 

 while other bacteria are blue. The whole process re- 

 quires from three to flve minutes. By this method 



